<style>
    #map {
        position: absolute;
        left: 25%;
        top: 0;
        bottom: 0;
        width: 75%;
    }
    .map-overlay {
        position: absolute;
        width: 25%;
        top: 0;
        bottom: 0;
        left: 0;
        font: 12px/20px 'Helvetica Neue', Arial, Helvetica, sans-serif;
        background-color: #fff;
        max-height: 100%;
        overflow: hidden;
    }

    .map-overlay fieldset {
        display: none;
        background: #ddd;
        border: none;
        padding: 10px;
        margin: 0;
    }

    .map-overlay input {
        display: block;
        border: none;
        width: 100%;
        border-radius: 3px;
        padding: 10px;
        margin: 0;
        box-sizing: border-box;
    }

    .map-overlay .listing {
        overflow: auto;
        max-height: 100%;
    }

    .map-overlay .listing > * {
        display: block;
        padding: 5px 10px;
        margin: 0;
    }

    .map-overlay .listing a {
        border-bottom: 1px solid rgba(0, 0, 0, 0.1);
        color: #404;
        text-decoration: none;
    }

    .map-overlay .listing a:last-child {
        border: none;
    }

    .map-overlay .listing a:hover {
        background: #f0f0f0;
    }
</style>

<div id="map"></div>

<div class="map-overlay">
    <fieldset>
        <input
            id="feature-filter"
            type="text"
            placeholder="Filter results by name"
        />
    </fieldset>
    <div id="feature-listing" class="listing"></div>
</div>

<script>
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v11',
        center: [-98, 38.88],
        maxZoom: 5,
        minZoom: 1,
        zoom: 3
    });

    // Holds visible airport features for filtering
    var airports = [];

    // Create a popup, but don't add it to the map yet.
    var popup = new mapboxgl.Popup({
        closeButton: false
    });

    var filterEl = document.getElementById('feature-filter');
    var listingEl = document.getElementById('feature-listing');

    function renderListings(features) {
        var empty = document.createElement('p');
        // Clear any existing listings
        listingEl.innerHTML = '';
        if (features.length) {
            features.forEach(function(feature) {
                var prop = feature.properties;
                var item = document.createElement('a');
                item.href = prop.wikipedia;
                item.target = '_blank';
                item.textContent = prop.name + ' (' + prop.abbrev + ')';
                item.addEventListener('mouseover', function() {
                    // Highlight corresponding feature on the map
                    popup
                        .setLngLat(feature.geometry.coordinates)
                        .setText(
                            feature.properties.name +
                                ' (' +
                                feature.properties.abbrev +
                                ')'
                        )
                        .addTo(map);
                });
                listingEl.appendChild(item);
            });

            // Show the filter input
            filterEl.parentNode.style.display = 'block';
        } else if (features.length === 0 && filterEl.value !== '') {
            empty.textContent = 'No results found';
            listingEl.appendChild(empty);
        } else {
            empty.textContent = 'Drag the map to populate results';
            listingEl.appendChild(empty);

            // Hide the filter input
            filterEl.parentNode.style.display = 'none';

            // remove features filter
            map.setFilter('airport', ['has', 'abbrev']);
        }
    }

    function normalize(string) {
        return string.trim().toLowerCase();
    }

    function getUniqueFeatures(array, comparatorProperty) {
        var existingFeatureKeys = {};
        // Because features come from tiled vector data, feature geometries may be split
        // or duplicated across tile boundaries and, as a result, features may appear
        // multiple times in query results.
        var uniqueFeatures = array.filter(function(el) {
            if (existingFeatureKeys[el.properties[comparatorProperty]]) {
                return false;
            } else {
                existingFeatureKeys[el.properties[comparatorProperty]] = true;
                return true;
            }
        });

        return uniqueFeatures;
    }

    map.on('load', function() {
        map.addSource('airports', {
            'type': 'vector',
            'url': 'mapbox://mapbox.04w69w5j'
        });
        map.addLayer({
            'id': 'airport',
            'source': 'airports',
            'source-layer': 'ne_10m_airports',
            'type': 'symbol',
            'layout': {
                'icon-image': 'airport-15',
                'icon-padding': 0,
                'icon-allow-overlap': true
            }
        });

        map.on('moveend', function() {
            var features = map.queryRenderedFeatures({ layers: ['airport'] });

            if (features) {
                var uniqueFeatures = getUniqueFeatures(features, 'iata_code');
                // Populate features for the listing overlay.
                renderListings(uniqueFeatures);

                // Clear the input container
                filterEl.value = '';

                // Store the current features in sn `airports` variable to
                // later use for filtering on `keyup`.
                airports = uniqueFeatures;
            }
        });

        map.on('mousemove', 'airport', function(e) {
            // Change the cursor style as a UI indicator.
            map.getCanvas().style.cursor = 'pointer';

            // Populate the popup and set its coordinates based on the feature.
            var feature = e.features[0];
            popup
                .setLngLat(feature.geometry.coordinates)
                .setText(
                    feature.properties.name +
                        ' (' +
                        feature.properties.abbrev +
                        ')'
                )
                .addTo(map);
        });

        map.on('mouseleave', 'airport', function() {
            map.getCanvas().style.cursor = '';
            popup.remove();
        });

        filterEl.addEventListener('keyup', function(e) {
            var value = normalize(e.target.value);

            // Filter visible features that don't match the input value.
            var filtered = airports.filter(function(feature) {
                var name = normalize(feature.properties.name);
                var code = normalize(feature.properties.abbrev);
                return name.indexOf(value) > -1 || code.indexOf(value) > -1;
            });

            // Populate the sidebar with filtered results
            renderListings(filtered);

            // Set the filter to populate features into the layer.
            if (filtered.length) {
                map.setFilter('airport', [
                    'match',
                    ['get', 'abbrev'],
                    filtered.map(function(feature) {
                        return feature.properties.abbrev;
                    }),
                    true,
                    false
                ]);
            }
        });

        // Call this function on initialization
        // passing an empty array to render an empty state
        renderListings([]);
    });
</script>
